1. Field of the Invention
The present invention relates to a forced draft direct vent type room heater which forcibly supplies air for combustion and exhausts a combusted gas.
2. Description of the Related Art
Conventionally, such a room heater is known as is described in Japanese Utility Model Laid-Open No. 55-94647. This room heater has a burner housed in a combustion housing provided in an outer case. In the combustion housing, air for combustion is supplied and a combusted gas is exhausted by a combustion fan. In an exhaust path for exhausting the combusted gas therethrough, a main heat exchanger is provided in the upper stream side, and a supplementary heat exchanger is provided in the down stream side. In the outer case, an air intake and a vent hole are provided. In the outer case, a warm air fan is provided, and this warm air fan takes in room air from the air intake and sends the air to the inside of the room from the vent hole through the main heat exchanger and the supplementary heat exchanger.
In the above described official bulletin, the supplementary heat exchanger is arranged in the back side of the main heat exchanger. The room air flows to the vent hole through an air flow passage in the back side and an air flow passage in the front side of the main heat exchanger. Thereby, the room air flowing in the air flow passage in the back side is heated by the main heat exchanger and the supplementary heat exchanger.
In addition, a damper which can freely block the flow of the room air is provided in the air flow passage in the back side in the inner part of the outer case. The damper passes the room air to both of the air flow passages in the front side and the back side, when the length of an exhaust extension tube connected to the downstream end of the exhaust path is short. When the length of the exhaust extension tube is long, the damper blocks the flow of the room air flowing into the air flow passage in the back side. This aims at lowering the heat exchange efficiency of the room heater itself and raising the temperature of the combusted gas flowing into the exhaust extension tube, because when the exhaust extension tube provided in the room is long, a heat released from the exhaust extension tube also contributes to heating of the inside of the room.
By the way, a room heater also is recently required to provide higher efficiency as a measure against global warming. Here, in the above described conventional example, even when the length of the exhaust extension tube is long, the heat exchange efficiency is improved better by a method of passing room air to both of the air flow passages in the front side and in the back side. Accordingly, regardless of the length of the exhaust extension tube, it is advantageous for increasing the efficiency to pass the room air through both of the air flow passages in the front side and in the back side.
However, in the above described conventional example, the room air flowing into the air flow passage in the back side of the main heat exchanger results in being heated by the supplementary heat exchanger in a state of having been heated by the main heat exchanger. For this reason, the heat exchange efficiency of the supplementary heat exchanger is not enhanced so much.
In addition, there is occasionally employed a structure of providing a drain dish for making a drain formed in the exhaust extension tube flow into itself in the outer case, and passing the room air (warm air) which is heated by the heat exchanger to a section in which the drain dish is arranged to evaporate the drain in the drain dish. In this case, it causes the following problem when the heat exchange efficiency is enhanced. That is, in a weak combustion period, the temperature of the combusted gas flowing in the exhaust extension tube is excessively lowered, so that an amount of the formed drain exceeds an amount of an evaporated drain, and the drain overflows from the drain dish. In order to prevent the overflow of the drain from the drain dish, it is necessary to shorten the length of the exhaust extension tube and to reduce the amount of the formed drain. As a result, a position where the room heater can be set becomes limited.